The present invention relates to grease guns and more particularly to a grease gun having a pressure relief valve assembly which releases air in the dispensing pump, which air retards flow of lubricant from the gun. It is well known that when air bubbles, in sufficient quantity, are drawn into the cylinder of a dispensing pump the next stroke will not cause the grease to flow from the dispensing nozzle. The reason is that air is compressible and the dispensing stroke of the piston will compress the air, but the pressure of the compressed air is not great enough to push grease out of the nozzle. The result is a blockage or vapor lock within the pump which makes the grease gun inoperable.
A variety of machinery requires frequent lubrication while in operation. For example, farm machinery in use in a remote location employs portable manual grease guns for lubrication several times daily. Often, air becomes entrapped in the gun and forms an air pressure pocket which prevents the flow of grease as indicated above. The operator can disassemble the gun to bleed the air but more often, time dictates that the plugged gun be set aside and another gun used instead. Thus, several grease guns are customarily filled each day and carried to the work site.
Heretofore, pressure relief valves have been installed on high pressure grease guns to relieve the delivery pressure when the gun is not in operation (U.S. Pat. Nos. 4,062,425; 4,063,618 and 3,788,427). Air pressure built-up at the delivery tube or extension of a manually operated grease gun has not been recognized as a serious problem in the art nor have solutions thereto been proposed.
The present invention provides an efficient and simple solution to this air pressure pluggage problem which makes it especially convenient for the operator in the field to quickly restore operation of the gun. Thus, the operator need spend little time in handling the grease gun should an air pressure pluggage occur and he can devote more time to operation of the machinery.